Introduction to ecosystems

Week 1: What is an ecosystem?

Introduction

Throughout this course you will be considering these overarching questions:

What is the importance of understanding ecosystems?

How do they work?

How crucial is their conservation?

But first, what constitutes an ecosystem and how is an ecosystem defined? Consider the habitats shown in Figure 1. Are they individual ecosystems or groups of ecosystems? Could there be different ways of defining ecosystems?

By the end of this first week you will be able to explain how an ecosystem is defined, in terms of energy flow, and be able to define and use terms which are introduced in the videos and text and apply them to new situations and examples where appropriate.

There is more than one way in which an ecosystem can be defined. In the following video Dr Mike Gillman highlights the difference between two schools of thought. One definition is that an ecosystem is an area where groups of organisms experience similar conditions.

Alternatively, an ecosystem is a living system of energy transfer, a whole complex of organisms living together, linked by energy transfer. The key difference is that ‘area’ defines one, whereas ‘energy relationships’ define the other.

Before we can begin to tackle the larger issues of ecosystems and how they have been compromised by human intervention, we must understand what is meant by ‘ecosystem’. As you watch the video ‘What is an ecosystem?’, consider the following questions, which we will discuss in the next section:

What is the key difference between the definitions?

What is the working definition of ‘ecosystem’ that we are going to use in this course?

Transcript

What is an ecosystem?

DR MICHAEL GILLMAN

Ecosystem-- what is it? What does it mean? How can we define what an ecosystem actually is? Well, there are two ways of doing it-- two definitions, two schools of thought. In the red corner, supporters of a geographical definition. They would say that an ecosystem is an area where groups of organisms experience similar conditions. These guys talk about the rainforest ecosystem, the Arctic ecosystem, that sort of thing. Defined like this, ecosystems tend to be, well, big. It's a widely used definition. You'll have heard politicians talk about ecosystems like that. And conservation groups tend to do the same thing. On the other hand, over here in the blue corner are people who prefer a different definition. These people say, it's not just an area, it's a living system of energy transfer, of nutrients being passed up and passed on. It's all about the system itself, not the box it comes in. This is the approach that would have been favoured by one of the founding fathers of the science of ecology, Sir Arthur Tansley. His view of an ecosystem revolved around his concept of the biome, which we would today call a community. He saw a community as being—

NARRATOR

"the whole complex of organisms naturally living together, whose life must be considered and studied as a whole."

DR MICHAEL GILLMAN:

Tansley's main interest was in plants, so his work and ideas tend to focus on them. He defined plant communities as--

NARRATOR

"--any collection of plants growing together which has a whole certain individuality."

DR MICHAEL GILLMAN

Tansley's ideas were controversial and much debated. But they found favour in North America and Europe and, today, form the basis of the British National Vegetation Classification. The key thing is Tansley's ideas of communities were not just about geographical location. They were about how species interact together. And so was born Tansley's definition of an ecosystem.

NARRATOR

"A wider conception still is to include, with the biome, all the physical and chemical factors of the biome's environment, or habitat, as parts of one physical system which we may call an ecosystem, because it's based on the oikos, or home, of a particular biome. All the parts of such an ecosystem, organic and inorganic, biome and habitat, may be regarded as interacting factors."

DR MICHAEL GILLMAN

So there it is. That's what we mean by an ecosystem. And for the purposes of this course, we'll define ecosystem as--

NARRATOR

"--a set of organisms and abiotic components, linked by processes of energy transfer and cycling of materials."

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